The general case is that you can't fix burnt out motors - very large and expensive motors might be rewired at a specialist company but not small tool motors - it's not economic - there's no demand and there's very probably nobody willing to do it.
New motors may be had - depending on finding a source of supply but you fail to mention anything about your specific tool.
You may well be better off junking it and buying a new one - whatever it is.
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix d.i.y tools.